This disclosure relates to a low differential, pilot-operated regulation apparatus and method and, more particularly, to such as system and method for regulating the pressure of fluid flowing through a pipeline.
Pilot operated regulators and regulation systems for controlling the fluid pressure in a pipeline downstream of the regulators are well known. For example, earlier designs of pilot- operated regulators used a variety of balanced valves, such as double port valves, balanced cage guided plugs, balanced pistons, and single port valves with balancing diaphragms. However, to accommodate different flow pressures, different size actuator casings had to be used along with different closing springs for each casing. Also, despite the fact that balanced valves were used, relative high shutoff forces and pressure differentials were required, especially by the larger valves. To reduce the minimum differential required to open the valve, the customer could select a larger diameter actuator, which was more expensive and was usually rated for lower pressures.
Moreover, many regulators of this type utilize pistons that reciprocate in a cylindrical chamber with a relatively tight seal ring extending between the outer surface of the piston and the corresponding inner wall of the chamber. However, considerable friction is introduced at the seal ring which compromises performance of the system.
Therefore what is needed is a regulator and method of the above type that offers both full capacity and bubble tight shut off for a relatively wide range of differential pressures without the need for different actuator casing sizes and closing springs. Also, need is a regulator and method of the above type which eliminates the use of actuator pistons operating against a relative tight seal that causes friction.
To this end, and according to an embodiment of the present invention, an apparatus and method are provided for regulating the pressure of fluid flowing though a conduit system according to which a valve seat is formed in a lower housing connecting in the conduit system with the seat extending between an upstream portion of the system and a downstream portion of the system. A valve stem is mounted in the lower housing for axial movement in the lower housing and one end of the stem is connected to a valve head so that the valve head cooperates with the seat in a manner to control the flow of fluid through the seat and through the lower housing and the conduit system. Two spaced membranes are mounted in the upper housing to define at least two chambers, and the membranes are connected to the valve stem in a manner so that movement of the membranes causes corresponding movement of the valve stem and the valve head relative to the valve seat to control the flow of fluid through the seat and through the lower housing and the conduit system. The downstream portion of the conduit system is connected to one of the chambers to apply a load to one of the membranes in proportion to the fluid pressure in the downstream portion so that changes in the fluid pressure in the downstream portion causes corresponding changes to the load on the one membrane, corresponding movement of the valve stem and the valve head, and corresponding changes to the fluid flow through the lower housing. The upstream portion of the conduit system is connected to the other chamber to apply a load to the other membrane in proportion to the fluid pressure in the upstream portion so that changes in the upstream pressure causes corresponding changes in the load on the other membrane, corresponding movement of the valve stem and the valve head, and corresponding changes to the fluid flow through the lower housing.